Posted on by Tammy Plotner

“Cool” Gas May Be At The Root Of Sunspots

During the initial stage of sunspot emergence and cooling, the formation of H2 may trigger a temporary "runaway" magnetic field intensification. The magnetic field prevents the flow of energy from inside the sun to the outside, and the sunspot cools as the energy shines into space. They form hydrogen molecules that take half the volume of the atoms, thus dropping pressure and concentrating the magnetic field, and so on. (adapted from Jaeggli, 2011; sunspot image by F. Woeger et al

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Although well over 40 years old, the Dunn Solar Telescope at Sunspot, New Mexico isn’t going to be looking at an early retirement. On the contrary, it has been outfitted with the new Facility Infrared Spectropolarimeter (FIRS) and is already making news on its solar findings. FIRS provides simultaneous spectral coverage at visible and infrared wavelengths through the use of a unique dual-armed spectrograph. By utilizing adaptive optics to overcome atmospheric “seeing” conditions, the team took on seven active regions on the Sun – one in 2001 and six during December 2010 to December 2011 – as Sunspot Cycle 23 faded away. The full sunspot sample has 56 observations of 23 different active regions… and showed that hydrogen might act as a type of energy dissipation device which helps the Sun get a magnetic grip on its spots.

“We think that molecular hydrogen plays an important role in the formation and evolution of sunspots,” said Dr. Sarah Jaeggli, a recent University of Hawaii at Manoa graduate whose doctoral research formed a key element of the new findings. She conducted the research with Drs. Haosheng Lin, also from the University of Hawaii at Manoa, and Han Uitenbroek of the National Solar Observatory in Sunspot, NM. Jaeggli now is a postdoctoral researcher in the solar group at Montana State University. Their work is published in the February 1, 2012, issue of The Astrophysical Journal.

You don’t have to be a solar physicist to know about the Sun’s 11 year cycle, or to understand how sunspots are cooler areas of intense magnetism. Believe it or not, even the professionals aren’t quite sure of how all the mechanisms work… especially those which cause sunspot forming areas that retard normal convective motions. Of the things we’ve learned, the spot’s inner temperature has a correlation with its magnetic field strength – with a sharp rise as the temperature cools. “This result is puzzling,” Jaeggli and her colleagues wrote. It implies some undiscovered mechanism inside the spot.

NOAA 11131 sunspot region (Dec. 6, 2010) was the most intense spot measured in this study, but far from the largest the Sun can produce. The two bottom images show the strength of the magnetic field (C) and the contrast between the interior of the spot and the surrounding photosphere (D). The first graph (A) shows how OH starts to appear in the penumbra and continues to rise as the magnetic field strength rises. Because OH forms at a lower temperature than H2, its presence implies the quantity of hydrogen molecules that could be present (B). (adapted from Jaeggli et al, 2012)

One theory is that hydrogen atoms combining into hydrogen molecules may be responsible. As for our Sun, the majority of hydrogen is ionized atoms because the average surface temperature is assessed at 5780K (9944 deg. F). However, since Sol is considered a “cool star”, researchers have found indications of heavy-element molecules in the solar spectrum – including surprising water vapor. These type of findings might prove the umbral regions could allow hydrogen molecules to combine in the surface layers – a prediction of 5% made by the late Professor Per E. Maltby and colleagues at the University of Oslo. This type of shift could cause drastic dynamic changes where gas pressure is concerned.

“The formation of a large fraction of molecules may have important effects on the thermodynamic properties of the solar atmosphere and the physics of sunspots,” Jaeggli wrote.

With direct measurements being beyond our current capabilities, the team then measured a proxy – the hydroxyl radical made of one atom each of hydrogen and oxygen (OH). According to the National Solar Observatory, “OH dissociates (breaks into atoms) at a slightly lower temperature than H2, meaning H2 can also form in regions where OH is present. By coincidence, one of its infrared spectral lines is 1565.2nm, almost the same as the 1565nm line of iron, used for measuring magnetism in a spot and one of the lines FIRS is designed to observe.”

Spectral lines are the unique "fingerprints in light" that all atoms and molecules produce. In the presence of a magnetic field in a hot gas, some lines split, betraying the presence and strength of the magnetic fields. Each line corresponds to electrons giving up energy in discrete amounts, or quanta, as light. Imposing a magnetic field on the atom makes the electrons produce multiple lines instead of one. The spread of these lines is a direct measure of the strength of the magnetic field, and is greater in the red and in the infrared spectrum. This image depicts sunspot spectra taken by FIRS with lines centered at 630.2nm (left) and 1564.8nm (right). Note the broadened area in the color ellipses, indicating line splitting inside a spot, and how the broadening is greater at the longer wavelength. Contrast is adjusted to enhance visibility in the inset boxes.

By combining both old and new data, the team measured magnetic fields across sunspots, and the OH intensity inside spots, judging the H2 concentrations. “We found evidence that significant quantities of hydrogen molecules form in sunspots that are able to maintain magnetic fields stronger than 2,500 Gauss,” Jaeggli commented. She also said its presence leads to a temporary “runaway” intensification of the magnetic field.

As for the anatomy of a sunspot, magnetic flux boils up from the Sun’s interior and slows surface convection – which in turns stops cooler gas which has radiated its heat into space. From there, molecular hydrogen is created, reducing the volume. Because it is more transparent than its atomic counterpart, its energy is also radiated into space allowing the gas to cool even more. At this point the hot gas primed by the flux compresses the cooler region and intensifies the magnetic field. “Eventually it levels out, partly from energy radiating in from the surrounding gas. Otherwise, the spot would grow without bounds. As the magnetic field weakens, the H2 and OH molecules heat up and dissociate back to atoms, compressing the remaining cool regions and keeping the spot from collapsing.”

For now, the team admits that additional computer modeling is required to validate their observations and that most of the active regions so far have been mild ones. They’re hoping that Sunspot Cycle 24 will give them more fuel to be “cool”…

Original Story Source: National Solar Observatory News Release.

Posted on by Irene Antonenko

New Insights into the Moon’s Mysterious Magnetic Field

Lunar Dynamo
Moon with cut-away showing stylized interior with dynamo and magnetic field lines.

Ever since the Apollo era, scientist have known that the Moon had some kind of magnetic field in the past, but doesn’t have one now. Understanding why is important, because it can tell us how magnetic fields are generated, how long they last, and how they shut down. New studies of Apollo lunar samples answer some of these questions, but they also create many more questions to be answered.

The lunar samples returned by the Apollo missions show evidence of magnetization. Rocks are magnetized when they are heated and then cooled in a magnetic field. As they cool below the Curie temperature (about 800 degrees C, depending on the material), the metallic particles in the rock line up along ambient magnetic fields and freeze in that position, producing a remnant magnetization.

This magnetization can also be measured from space. Studies from orbiting satellites show that the Moon’s magnetization extends well beyond the regions sampled by Apollo astronauts. All this magnetization means that the Moon must have had a magnetic field at some point in its early history.

Most of the magnetic fields we know of in the Solar System are generated by a dynamo. Basically, this involves convection in a metallic liquid core, which effectively moves the metal atoms’ electrons, creating an electric current. This current then induces a magnetic field. The convection itself is thought to be driven by cooling. As the outer core cools, the colder portions sink to the interior and let the warmer interior sections move outwards towards the exterior.

Because the Moon is so small, a magnetic dynamo that is driven by convective cooling is expected to have shut down some time around 4.2 billion years ago. So, evidence of magnetization after this time would need either 1) an energy source other than cooling to drive the motion of a liquid core, or 2) a completely different mechanism for creating magnetic fields.

Laboratory experiments have suggested one such alternate method. Large basin-forming impacts could produce short-lived magnetic fields on the Moon, which would be recorded in the hot materials ejected during the impact event. In fact, some observations of magnetization are located at the opposite side of the Moon (the antipode) from large basins.

So, how can you tell if magnetization in a rock was formed by a core dynamo or an impact event? Well, impact-induced magnetic fields last only about 1 day. If a rock cooled very slowly, it would not record such a short-lived magnetic field, so any magnetism it retains must have been produced by a dynamo. Also, rocks that have been involved in impacts show evidence of shock in their minerals.

One lunar sample, number 76535, which shows evidence of slow cooling and no shock effects, has a distinct remnant magnetization. This, along with the age of the sample, suggests that the Moon had a liquid core and a dynamo-generated magnetic field 4.2 billion years ago. Such a core dynamo is consistent with convective cooling. But, what if there are younger samples?

New studies recently published in Science by Erin Shea and her colleagues suggest this may be the case. Ms Shea, a graduate student at MIT, and her team studied sample 10020, a 3.7 billion year old mare basalt brought back by the Apollo 11 astronauts. They demonstrated that sample 10020 shows no evidence of shock in its minerals. They estimated that the sample took more than 12 days to cool, which is much slower than the lifetime of an impact-induced magnetic field. And they found that the sample is very strongly magnetized.

From their studies, Ms Shea and her colleagues conclude that the Moon had a strong magnetic dynamo, and therefore a moving metallic core, around 3.7 billion years ago. This is well after the time a convective cooling dynamo would have shut down. It is not clear, however, if the dynamo was continually active since 4.2 billion years ago, or if the mechanism that moved the liquid core was the same at 4.2 and 3.8 billion years. So, what other ways are there to keep a liquid core moving?

Recent studies by a team of French and Belgian scientists, led by Dr. Le Bars, suggest that large impacts can unlock the Moon from its synchronous rotation with the Earth. This would create tides in the liquid core, much like the Earth’s oceans. These core tides would cause significant distortions at the core-mantle boundary, which could drive large-scale flows in the core, creating a dynamo.

In another recent study, Dr. Dwyer and colleagues suggested that precession of the lunar spin axis could stir the liquid core. The early Moon’s proximity to the Earth would have made the Moon’s spin axis wobble. This precession would cause different motions in the liquid core and overlying solid mantle, producing a long-lasting (longer than 1 billion years) mechanical stirring of the core. Dr. Dwyer and his team estimate that such a dynamo would naturally shut down about 2.7 billion years ago as the Moon moved away from the Earth over time, diminishing its gravitational influence.

Unfortunately, the magnetic field suggested by the study of sample 10020 doesn’t fit either of these possibilities. Both these models would provide magnetic fields that are too weak to have produced the strong magnetization observed in sample 10020. Another method for mobilizing the liquid core of the Moon will need to be found in order to explain these new findings.

Sources:
A Long-Lived Lunar Core Dynamo. Shea, et al. Science 27, January 2012, 453-456. doi:10.1126/science.1215359.

A long-lived lunar dynamo driven by continuous mechanical stirring. Le Bars et al. Nature 479, November 2011, 212-214. doi:10.1038/nature10564.

An impact-driven dynamo for the early Moon. Dwyer et al. Nature 479, November 2011, 215-218. doi:10.1038/nature10565.

Posted on by Tammy Plotner

Quantum Levitation And The Superconductor

Superconductivity and magnetic fields are like oil and water… they don’t mix. When it can, the superconductor will push out any magnetic fields from the interior in a process called the Meissner effect. It happens when a sample is cooled below its superconducting transition temperature, where it then cancels out its magnetic flux. What’s next? A superconductor. Now the fun really begins… Continue reading “Quantum Levitation And The Superconductor”

Posted on by Tega Jessa

Permanent Magnet

Permanent Magnet
Super Magnets, the strongest type of permanent magnets

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A permanent magnet is a magnet that does not lose its magnet field. However what makes a magnet permanent? In order to understand this we need to know how magnets work. Magnetism is an aspect of the phenomenon known as the electromagnetic force a fundamental force of the physical universe. Magnetism like its other aspect electricity manifests itself as a field. What makes a magnet is when certain substances and elements are induced with a strong magnetic field. In the case of permanent magnets this field remains over time without weakening.

A permanent magnet is a magnet because of the orientation of its domains. Domains are the small magnetic field inherent in the crystalline structure of ferromagnetic materials. Ferromagnetic materials are the only substances capable of being made into magnets they are normally iron, nickel, or alloys that are made or rare-earth metals. A magnet is created when certain condition cause separate domains in a ferromagnetic item to be all aligned in the same direction. However the method used in most cases weak magnets can only be made. This is normally by direct contact with a naturally magnetic material or by running an electric current through it. However in the case of a field produced by rubbing it against a strong magnet is too weak and will fade over time as the domains return to their original positions.

The main way that permanent magnets are created is by heating a ferromagnetic material to a key high temperature. The temperature is specific to each kind of metal but it has the effect of aligning and “fixing” the domains of the magnet in a permanent position. It is conjectured that this same process inside the Earth is what creates natural permanent magnets.

Permanent magnets are important for their industrial uses especially when it comes to power generation and electric motors. The induction process for turbines and generators needs permanent magnets to turn mechanical motion into energy. They are also important for electric motors in many electronics using the reverse of the induction of electric current to make mechanical energy. As you can see without the permanent magnet we would not be able to take full advantage of the capabilities of electricity in modern devices.

We have written many articles about permanent magnets for Universe Today. Here’s an article about bar magnets, and here’s an article about super magnets.

If you’d like more info on permanent magnets, check out these articles from Hyperphysics and Practical Physics.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

References:
Hyperphysics
How Magnets Work

Posted on by Matt Williams

Paramagnetism

[/caption]Magnetism is a fundamental force of the universe, essential to its function and existence in the same way that gravity and weak and strong nuclear forces are. But interestingly enough, there are several different kinds of magnetism. For example, there is ferromagnetism, a property which applies to super magnets, where magnetic properties exist regardless of whether or not there is a magnetic field acting on the material itself. There is also Diamagnetism, which refers to materials that are not affected by a magnetic field, and Paramagnetism, a form of magnetism that occurs only in the presence of an externally applied magnetic field.

Materials that are called ‘paramagnets’ are most often those that exhibit, at least over an appreciable temperature range, magnetic susceptibilities that adhere to the Curie or Curie–Weiss laws. According to these laws, which apply at low-levels of magnetization, the susceptibility of paramagnetic materials is inversely proportional to their temperature. Mathematically, this can be expressed as: M = C(B/T), where M is the resulting magnetization, B is the magnetic field, T is absolute temperature, measured in kelvins, C is a material-specific Curie constant.

Paramagnets were named and extensively researched by British scientist Michael Faraday – the man who gave us Faraday’s Constant, Faraday’s Law, the Faraday Effect, etc. – beginning in 1845. He, and many scientists since, found that certain material exhibited what was commonly referred to as “negative magnetism”. Most elements and some compounds are paramagnetic, with strong paramagnetism being exhibited by compounds containing iron, palladium, platinum, and certain rare-earth elements. In such compounds atoms of these elements have some inner electron shells that are incomplete, causing their unpaired electrons to spin like tops and orbit like satellites. This makes the atoms act like a permanent magnet, tending to align with and hence strengthen an applied magnetic field. However, once the magnetic field is removed, the atoms fall out of alignment and the material return to its original state. Strong paramagnetism also decreases with rising temperature because of the de-alignment produced by the greater random motion of the atomic magnets.

Weak paramagnetism, independent of temperature, is found in many metallic elements in the solid state, such as sodium and the other alkali metals. Other examples include Iron oxide, Uranium, Platinum, Tungsten, Cesium, Aluminum, Lithium, Magnesium, Sodium, and Oxygen gas. Even iron, a highly magnetic material, can become a paramagnet once it is heated above its relatively high Curie-point.

We have written many articles about magnetism for Universe Today. Here’s an article about magnetic field, and here’s an article about what magnets are made of.

If you’d like more info on paramagnetism, check out these articles from Hyperphysics and Physlink.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
http://en.wikipedia.org/wiki/Paramagnetism
http://en.wikipedia.org/wiki/Faraday
http://www.britannica.com/EBchecked/topic/442927/paramagnetism
http://www.physlink.com/education/askexperts/ae595.cfm
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Posted on by Matt Williams

Magnetic Energy

Magnetic Energy
Magnetic Energy Flow. Image Credit: dhost.info

[/caption]During the 19th century, one of the greatest discoveries in the history of physics was made by an Scottish physicist named James Clerk Maxwell. It was at this time, while studying the perplexing nature of magnetism and electricity, that he proposed a radical new theory. Electricity and magnetism, long thought to be separate forces, were in actuality closely associated with each other. That is, every electrical current has associated with it a magnetic field and every changing magnetic field creates its own electrical current. Maxwell went on to express this in a set of partial differential equations, known as Maxwell’s Equations, and form the basis for both electrical and Magnetic Energy.

In fact, thanks to Maxwell’s work, magnetic and electric energy are more appropriately considered as a single force. Together, they are what is known as electromagnetic energy – i.e. a form of energy that has both electrical and magnetic components. It is created when one runs a magnetic current through a wire or any other conducive material, creating a magnetic field. The magnetic energy generated can be used to attract other metal parts (as in the case in many modern machines that have moving parts) or can be used to generate electricity and store power (hydroelectric dams and batteries).

Since the 19th century, scientists have gone on to understand that many types of energy are in fact forms of electromagnetic energy. These include x rays, gamma rays, visible light (i.e. photons), ultraviolet light, infrared radiation, radio waves, and microwaves. These forms of electromagnetic energy differ from each other only in terms of the wavelength and frequency. Those forms which have shorter waves and higher frequencies tend to be the more harmful varieties, such as x-rays and gamma rays, while those that have longer waves and shorter frequencies, such as radio waves, tend to be more benign.

In mathematical terms, the equation for measuring the output of a magnetic field can be expressed as follows: V = L dI/dt + RI where V is volume, L is inductance, R is resistance, I is charge, dI represents change in charge, and dt represents change over time.

Here are some articles about Magnetic Energy written for Universe Today.
Behind the Power and Beauty of Northern Lights
Magnetic Fields in Inter-cluster Space: Measured at Last

If you’d like more info on Magnetic Energy, check out these articles:
Wikipedia Entry on Magnetic Energy
More info about magnetic energy

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
http://en.wikipedia.org/wiki/Magnetic_energy
http://en.wikipedia.org/wiki/James_Clerk_Maxwell
http://en.wikipedia.org/wiki/Maxwell%27s_equations
http://fi.edu/guide/hughes/10types/typesmagnetic.html
http://farside.ph.utexas.edu/teaching/em/lectures/node84.html
http://science.jrank.org/pages/2489/Energy-Magnetic-energy.html

Posted on by Jerry Coffey

How Do Magnets Work

How Do Magnets Work
Bar Magnet

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We have all played with magnets from time to time. Every time you do, you have asked yourself ‘how do magnets work?’ Many of us understand that magnets have two different charges and that like charges repel each other, but that still does not explain how a magnet works. Below is an attempt to explain the basics behind the secret inner workings of the mysterious magnet.

A magnet is any material or object that produces a magnetic field. This magnetic field is responsible for the property of a magnet: a force that pulls on other ferromagnetic materials and attracts or repels other magnets. A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. Materials that can be magnetized, which are strongly attracted to a magnet, are called ferromagnetic. Although ferromagnetic materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field.

Some facts about magnets include:

  • the north pole of the magnet points to the geomagnetic north pole (a south magnetic pole) located in Canada above the Arctic Circle.
  • north poles repel north poles
  • south poles repel south poles
  • north poles attract south poles
  • south poles attract north poles
  • the force of attraction or repulsion varies inversely with the distance squared
  • the strength of a magnet varies at different locations on the magnet
  • magnets are strongest at their poles
  • magnets strongly attract steel, iron, nickel, cobalt, gadolinium
  • magnets slightly attract liquid oxygen and other materials
  • magnets slightly repel water, carbon and boron

The mechanics of how do magnets work really breaks right down to the atomic level. When current flows in a wire a magnetic field is created around the wire. Current is simply a bunch of moving electrons, and moving electrons make a magnetic field. This is how electromagnets are made to work.

Around the nucleus of the atom there are electrons. Scientists used to think that they had circular orbits, but have discovered that things are much more complicated. Actually, the patterns of the electron within one of these orbitals takes into account Schroedinger’s wave equations. Electrons occupy certain shells that surround the nucleus of the atom. These shells have been given letter names K,L,M,N,O,P,Q. They have also been given number names, such as 1,2,3,4,5,6,7(think quantum mechanics). Within the shell, there may exist subshells or orbitals, with letter names such as s,p,d,f. Some of these orbitals look like spheres, some like an hourglass, still others like beads. The K shell contains an s orbital called a 1s orbital. The L shell contains an s and p orbital called a 2s and 2p orbital. The M shell contains an s, p and d orbital called a 3s, 3p and 3d orbital. The N, O, P and Q shells each contain an s, p, d and f orbital called a 4s, 4p, 4d, 4f, 5s, 5p, 5d, 5f, 6s, 6p, 6d, 6f, 7s, 7p, 7d and 7f orbital. These orbitals also have various sub-orbitals. Each can only contain a certain number of electrons. A maximum of 2 electrons can occupy a sub-orbital where one has a spin of up, the other has a spin of down. There can not be two electrons with spin up in the same sub-orbital(the Pauli exclusion principal). Also, when you have a pair of electrons in a sub-orbital, their combined magnetic fields will cancel each other out. If you are confuse, you are not alone. Many people get lost here and just wonder about magnets instead of researching further.

When you look at the ferromagnetic metals it is hard to see why they are so different form the elements next to them on the periodic table. It is generally accepted that ferromagnetic elements have large magnetic moments because of un-paired electrons in their outer orbitals. The spin of the electron is also thought to create a minute magnetic field. These fields have a compounding effect, so when you get a bunch of these fields together, they add up to bigger fields.

To wrap things up on ‘how do magnets work?’, the atoms of ferromagnetic materials tend to have their own magnetic field created by the electrons that orbit them. Small groups of atoms tend to orient themselves in the same direction. Each of these groups is called a magnetic domain. Each domain has its own north pole and south pole. When a piece of iron is not magnetized the domains will not be pointing in the same direction, but will be pointing in random directions canceling each other out and preventing the iron from having a north or south pole or being a magnet. If you introduce current(magnetic field), the domains will start to line up with the external magnetic field. The more current applied, the higher the number of aligned domains. As the external magnetic field becomes stronger, more and more of the domains will line up with it. There will be a point where all of the domains within the iron are aligned with the external magnetic field(saturation), no matter how much stronger the magnetic field is made. After the external magnetic field is removed, soft magnetic materials will revert to randomly oriented domains; however, hard magnetic materials will keep most of their domains aligned, creating a strong permanent magnet. So, there you have it.

We have written many articles about magnets for Universe Today. Here’s an article about bar magnets, and here’s an article about super magnets.

If you’d like more info on magnets, check out some cool experiments with magnets, and here’s a link to an article about super magnets by Wise Geek.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
Wise Geek
Wikipedia: Magnet
Wikipedia: Ferromagnetism

Posted on by Tega Jessa

What are Magnets Made Of

Magnet
Magnet

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Magnets are the unsung heroes of the Modern Age. However most people don’t really understand what are magnets made of and how they even work. The issue is that we just know that magnets attract iron and nickel. However, magnets have a very interesting origin and can be seen as a physical manifestation of the electromagnetic force.

All magnets are made of a group of metals called the ferromagnetic metals. These are metals such as nickel and iron. Each of these metals have the special property of being able to be magnetized uniformly. When we ask how a magnet works we are simply asking how the object we call a magnet exerts it’s magnetic field. The answer is actually quite interesting.

In every material there are several small magnetic fields called domains. Most of the times these domains are independent of each other and face different directions. However, a strong magnetic field can arrange the domains of any ferromagnetic metal so that they align to make a larger and stronger magnetic field. This is how most magnets are made.

The major difference among magnets is whether they are permanent or temporary. Temporary magnets lose their larger magnetic field over time as the domains return to their original positions. The most common way that magnets are produced is by heating them to their Curie temperature or beyond. The Curie temperature is the temperature at which a ferromagnetic metals gains magnetic properties. Heating a ferromagnetic material to its given temperature will make it magnetic for a while. While heating it beyond this point can make the magnetism permanent. Ferromagnetic materials can also be categorized into soft and hard metals. Soft metals loses their magnetic field over time after being magnetized while hard metals are likely candidates for becoming permanent magnets.

Not all magnets are manmade. Some magnets occur naturally in nature such as lodestone. This mineral was used in ancient times to make the first compasses. However, magnets have other uses. With the discovery of the relation between magnetism and electricity, magnets are now a major part of every electric motor and turbine in existence. Magnets have also been used in storing computer data. There is now a type of drive called a solid state drive that allows data to still be saved more efficiently on computers.

We have written many articles about magnets for Universe Today. Here’s an article about the Earth’s magnetic field, and here’s an article about the bar magnet.

If you’d like more info on Magnets, check out NASA’s Discussion on Magnets, and here’s a link to an article about Magnetic Fields.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
NASA
Wikipedia

Posted on by Jean Tate

Electromagnetism

The short version: electromagnetism is one of the four fundamental forces (the strong force, the weak force, and gravitation are the other three), responsible for all magnetic, electrical, and electromagnetic phenomena.

The long version is a little more complicated.

Start with history … phenomena we today call electrical have been known for millennia (e.g. static electricity), as have their magnetic counterparts (e.g. lodestone). The 17th and 18th centuries saw considerable scientific study of each, as separate forces, with Ørsted and Ampère uniting the two into electromagnetism, around 1820. Maxwell consolidated (in 1864) everything known about electromagnetism into what today we call Maxwell’s equations … and predicted electromagnetic waves (or radiation), a prediction verified by Hertz, two decades later. However, Maxwell’s equations opened a can of worms (to do with the aether, and the speed of light) … which lead to Einstein and special relativity. In parallel, a series of discoveries lead to photons (the quanta of electromagnetic radiation) and quantum mechanics, and these in turn to the recognition that the spectacular success of classical electromagnetism (i.e. Maxwell’s equations) actually depends on quantum field theory (with all its counter-intuitives).

Fast forward to the 1940s, and Quantum Electrodynamics (QED), which has electrically charged particles interacting via exchanges of photons (real or virtual), and describes all electromagnetic phenomena. QED is the most successful theory in physics, period (it has been tested, and found accurate, to one part in 1012!).

Here’s a fun fact: QED incorporates special relativity … and an electric charge (with no magnetic field) becomes an electric current (with an associated magnetic field), in relativity, simply by switching to a frame of reference moving with respect to the (stationary) electrical charge.

So, in its classical form, electromagnetism is an instantaneous ‘action at a distance’ type of force; in its quantum form; it’s an exchange of virtual photons, at the speed of light.

Now for more complication.

In 1979 Sheldon L. Glashow, Abdus Salam, and Steven Weinberg shared the Nobel Prize for Physics, for their contributions to the unification of electromagnetism and the weak force … which goes under the name electroweak interaction. So electromagnetism is just one manifestation of something more general, just as electricity and magnetism are two manifestations of one underlying thing, electromagnetism.

Want to learn more? Try Stargazers’ Electromagnetism, Math Pages on Maxwell’s equations, Richard Feynman’s excellent non-technical book on QED, and the 1979 Nobel Press Release on the electroweak interaction.

To get a handle on how diverse the roles of electromagnetism are, in astronomy, check out these Universe Today articles (just some of the many): Stellar Jets are Born Knotted,
Magnetic “Ropes” Connect the Northern Lights to the Solar Wind, and Spitzer Spies Ghostly Magnetar.

Astronomy Cast has an episode devoted to electromagnetism, called Electromagnetism. Some others you may also find interesting, on this topic, are The Search for the Theory of Everything, and The Important Numbers in the Universe.

Sources:
Wikipedia
University of Oregon
NASA